Steve,
Some experience with pigs that may help: 1) Foam pigs come in a variety of forms. You get very soft ones (called swabbing pigs) and some that are surprisingly hard. The swabbing pigs are used to mop up water in gas pipelines after hydrotesting. My expectation is that you will pig this line a number of times, the first ones with great care, starting with the pig that is the safest and progressing up the line as you build confidence. When you run your first pig do not be conned into believing that a stiff foam pig is the only one available if your supplier does not have one. There ARE soft pigs to be had, not much stiffer than a bath sponge. So find a supplier that has them. 2) Also be aware of the force behind pigs, it is huge. Lets assume your pig sticks. If your line is a 300NB line it takes only 140 kPa or 14m of head across the pig to develop a force of one tonne. I have never yet heard of one not finding its way through. In fact I have heard of 4" pigs going missing down 2" lines and being found years later in vessels in other parts of the plant. Pigging can be fun, particularly when the pig gets lost..
Go slowly, and measure everything you can as the run takes place. I would definitely record the pressure on both sides of the line during the complete run of every run. I would also measure flow if I could. TO MEASURE IS TO KNOW. You seem to understand that.
Cheers,
Gordon
"Steve McKenzie" <mechproj@xtra.co.nz>
01/03/2004 09:06 PM
Please respond to PipingDesign
To: <PipingDesign@yahoogroups.com>
cc:
Subject: RE: [PipingDesign] Pipeline Pressure Survey
Hi Gordon
thanks for your thoughts.
Oddly enough, a foam pig appears the most attractive option to me because
if
it jams, it might fall to bits thereby not blocking the line. A variable
diameter piston pig could get me in the shit big time if it stuck.
Thanks for surfing for me; I appreciate it.
My idea of the recording tennis ball was a non-invasive pressure audit.
Once
we start pressing on the pipe walls, e.g. pig, the observed pressure
becomes
a function of pig drag. Now theres an expression!
I agree that I am not the first person with this problem. I guess I am fishing for a response to why we cant crack it.
Always the optimist.
Thanks again
Steve
-----Original Message-----
From: Gordon.Reddek@Alcan.com [mailto:Gordon.Reddek@Alcan.com]
Sent: Friday, February 27, 2004 11:58 AM
To: PipingDesign@yahoogroups.com
Subject: Re: [PipingDesign] Pipeline Pressure Survey
Steve,
There are things called intelligent pigs and are generally very expensive
to run. Search the web under "intelligent pigs" to find the companies that
own them.
I have never heard of a pig that does not take up the full diameter of the
line and which is not pushed along by the fluid. The type you describe
may exist. There are heaps of non intelligent pigs around mind you,
starting from soft foam pigs that will squeeze through just about any
restriction in a line, to special pigs designed to scrape and clean lines.
I imagine you would start with a pig that collapses to a very small
diameter with the first run. A foam pig would most probably not be a good
idea for that run because it is likely to be torn to shreds. There must
be a cup type pig that collapses to a small diameter. Quite often the
wear on the pig tells you what is going on.
You may find the device you are looking for but I can not help thinking
you are not the first with this problem. If you have not yet spoken to a
large pig manufacturer may I suggest you give it a burl. Those guys live
with your problem every day of their lives. I surfed Google with the
words "piping" and "pig" and came up with this site straight off:
http://www.pipingspecialties.com/UltraFlex.htm There are heaps like it.
Good luck
Gordon
"Steve McKenzie" <mechproj@xtra.co.nz>
26/02/2004 08:52 PM
Please respond to PipingDesign
To: PipingDesign@yahoogroups.com
cc:
Subject: [PipingDesign] Pipeline Pressure Survey
Gents
I have a 250/300NB gravity driven water pipeline about 9km long which
does not flow as much as expected. Some of the line is steel, for
pressure reasons, and the rest is PVC. The total friction head loss
is around 100m at around 75 l/s. A pressure/ R.L./line length survey
tells me that excessive scaling of the steel portions of the pipeline
are probably to blame. However I cannot rule out the possibility of a
few localised blockages in the line instead of relatively even
scaling.
To discount the localised blockage, I thought about sending a
pressure transmitter,timeclock and datalogger assembly down the line.
It would give me a pressure vs time profile for the line. Because I
know the flowrate, line profile and approximate velocity, an analysis
of the logged data should enable me to know if and where any
blockages are likely to be.
I know some pigs have this capability, but I am thinking more of
something about the size of a tennis ball, neutral buoyancy, and
hopefully with a screamer alarm so we can find it if it gets stuck.
Anyone know of anything suitable, or another way?
Cheers
Steve
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[Non-text portions of this message have been removed] Received on Mon Mar 01 17:47:00 2004
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